Electrical extension plug



O W I 5/ I J. HAMILTON ELECTRICAL EXTENSION PLUG Filed. Sept.

May 20, 1924.

Patented May 2O, 1924.

UNITED STATES PATENT OFFICE.

JOHN HAMILTON, 0F BOSTON, MASSACHUSETTS.

ELECTRICAL EXTENSION PLIIG.

Application filed September 27, 1919. Serial No. 326,793.

To all whom it may concern: Be it known that I, JOHN HAMILTON, 0

140 Bellevue Street, IVest Roxbury Station,

.material having two contact prongs or fingers which are intended to be pushed into small holes in a receptacle or fixed portion which is permanently connected to the cir cuit wiring. Practically all of the existing extension plugs are so designed that their contact making function depends upon a pushing force required to snap the projecting contacts of the cap portion into engagement with the contacts within the receptacle or fixed portion, and conversely a pull serves to separate the two portions.

Experience has shown that when using devices which are connected to an electric circuit by existing extension plugs great an noyance and trouble are caused by inadv'ertently pulling upon the extension wires and so causing the extension plug to disengage from the receptacle and fall, and in most cases in'industrial plants where heavy flexible cord is used with the portable devices the weight' of the cord itself is sufficient to cause the plug or cap to become disengaged; in many cases this leads to the breaking and destroying of the cap or plug by the consequent fall and in every case to an interference with the operations being conducted.

The objects of my invention are to eliminate this loss and delay by making the falling out of the plug impossible; this, I accomplish by making the contact making function of my extension plug depend upon a pull instead of a push consequently any strain which may be inadvertently applied to the extension wires will'tend to more securely engage rather than disengage the plug or cap.

In the accompanying drawing Figure 1 shows a front elevation; Figure 2 shows an end elevation and Figure 3 shows a plan; in each figure identlcal parts are similarly lettered and the lower or right handend of.

each view is shown in section.

X is a common conduit pipe fitting such as is commonly used in all kinds of electrical installations where the wiring is installed in conduits; ascommonly used X is fitted" with anyone of a variety of covers each one forming a special outlet for the wires within the conduit system.

In Figures 1, 2 and 3. is shown a new design of a cover for this standard pipe fitting and this forms part of my invention; I is the integrally formed iron cover with its ends bent up into hook like formation the whole resembling the letter G of the alphabet; the cover I is attached to the pipe fitting X, by the fastening screws D; into each of the hood like endsof the cover I is slipped a porcelain bushing or lining P and this is held in position by nuts recessed into the porcelain and engaging the fastening screws A which pass through the cover I.

This porcelain lining P carries at its upper end and enclosed within the projecting walls or cars of both I and P a common U shaped spring contact clip Esuch as is used with standard cartridge'fuses a sheet brass contact strip B is bent so as to liewithin the porcelain lining P and to connect the.

contact clip E with the wire from withinithe pipe fitting X, which wire comes through a hole in the cover I and the porcelain P and is held in contact with the connecting strip B by the contact screw W. The screws C whose heads are recessed into the porcelain P engage the contact strip 13 (one'of them passing through the contact clip E) and hold the electrical elements rigidly within the porcelain P; this description applies to either end of the cover I both ends being identical. i

F is a cylindrically formed hollow contact carrier made of insulating material except that its ends are fitted with removable metal contact ferrules such as are used on the standard cart-ridge fuses for the purpose of engaging the spring contact clips E. In Figure 1F is shown fitted with a hollow grip or handle of insulating material H: by taking hold of H F may be pulled against resistance into position in engagement with the spring contact clips E as shown in Figure 1 or forcibly removed therefrom.

Also in Figure 1 are shown extension wires extending from the ferrule contacts on F through the hollow handle H to contact with terminals of lamp suitably mounted on portable handle M.

It will be noted from these illustrations that pulling upon the handle H or the portable lamp handle M or upon the extenslon wires connecting these two will tend to seat rather than unseat the contact carrier F. Although I have illustrated my extenslon .plug in combination with an incandescent electric lamp I have no intention of limiting its use to lighting but on the contrary have in mind its use for all forms of tools and machinery.

Having thus fully described my invention what I claim as new and wish to protect bv Letters Patent is as follows 1. In combination an electric conduit fitting li aving a removable cover formed so as to provide a hooded shelter. at each end; a lining of insulating material within the hooded shelters; U shaped spring contacts mounted on the insulating linings within the hooded shelters; a means for connecting wires from the inside of the conduit fitting to the U shaped spring contacts; a cylin drically formed plug fitted with a ferrule contact at each end and said ferrules adapted to snap into spring engagement with the U shaped spring contacts and to mainta n this spring engagement in all possible positions of the plu a handle mounted upon this plug and wires passing from the ferrule contacts through the plug and handle to a portable translating device.

2. In combination an electric conduit fitting with its removable cover carrying concealed electric U shaped spring contacts mounted in aninverted position; means for connecting wires from the inside of the conduit' fitting to said .Ushaped contacts; an elongated tubular bridging plug carrying a ferrule contact at each end; said ferrule con tacts adapted to snap by direct pressure into the spring embrace of said U shaped contacts; a lever handle mounted upon said bridging plug so as to project at right angles to its tubular axis and wires leading from said ferrule contacts through said handleto a translating device substantially as shown.

3. Inan electric circuit extension device a fixed portion consisting of a hollow oblong casing of insulating 1naterial having a transverse section cut from its upper wall and inverted T sections out from its side walls; a double claw shaped spring metal contact mounted in its interior at either side of the opening in the upper wall; means for connecting main circuit wires to said claw shaped contacts; a movable plug portion of insulating material having a contact fitted on each end adapted to be snapped into the embrace of said double claw shaped'spring metal contacts; a handle mounted upon said movable plug portion at right angles to it and so disposed that when in service it projects upwards through the opening in the upper wall of said fixed portion and wires connected to the contacts on said movable portion and passing through its in terior and that of the handle to a translating device substantially as shown.

4:. In combination an electric receptacle having U shaped spring'contacts mounted on the lower side of the upperor front wall of the receptacle with their openings pointing inwardly; a tubular plug having a handle mounted upon it at right angles to its tubular axis; contacts mounted upon said tubular plug s'o as to engage said U shaped spring contacts and wires leading from said plug contacts through said handle to a translating device substantially as shown.

5. An electric circuit extension device consisting of a fixed portion and a portableportion made of insulating material; said fixed portion fitted with spring metal contacts equipped with a means for connecting same to main circuit wires; said portable portion consisting of a cylindrical plug fitted with ferrule contacts adapted to snap by a direct push or pull into or out of electrical engage ment with said spring metal contacts on said fixed portion and to be revoluble through 180 while maintaining said electrical engagement; a handle mounted upon said port able portion and wires passingfrom said ferrule contacts through said handle to a translating device substantially as shown.

6. As an article of manufacture an electric circuit extension device consisting of a fixed and a movable portion both being made of insulating material; said fixed portion consisting of a hollow oblong casing with a transverse opening on' its upper wall and inverted T sections cut from its side walls; spring clip contacts mounted at either side of the opening in the upper wall; means for connecting wires to said spring clip contacts; said movable portion consisting of an elongated cylindrical plug having a ferrule contact on either end and a handle projecting at. rightangles; said ferrule contacts adapted to be snapped into or out of engagement with said spring -clips in the fixed portion by means of a direct pull or push on said handle and wires leading from said ferrule contacts to a translating device substantially as shown.

In testimony whereof I have affixed my signature.

JOHN HAMILTON. 

